Invertebrates: Phylum Porifera

1. Invertebrates: Phylum Porifera • Sponges • Multicellular; body a loose aggregate of cells • All aquatic, mostly marine • Body with pores (ostia), canals, and chambers for circulation of water • Epidermis of flat cells, some with contractile fibers • Middle layer is semi-fluid, with wandering amebocytes • Inner layer of choanocytes-flagellated to move water

2. Phylum Poriferacont’d • Filter feeders- intracellular digestion • Cells get food from circulating water • Classified based on skeleton • Composed of spicules • Chalk sponges - spicules of calcium carbonate • Glass sponges - spicules of silica • Proteinaceous sponges - spongin fibers • Reproduction • asexual by budding, sexual by fusion of gametes

3. Sponge • Fig. 30.3

4. Invertebrates: Phylum Cnidaria • Cnidarians • Multicellular, tubular or bell-shaped animals-radial symmetry • All aquatic, mostly marine • 2 germ layers during development • Organized at tissue level • Nematocysts • stinging cells unique to cnidarians

5. Cnidarians cont’d • 2 body types-polyps and medusae • Life cycle alternates between both forms in some; in others one form is reduced or absent • Gastrovascular cavity-sac-like body plan • Includes corals, jellyfish, and hydrozoans • Corals- polyps • Jellyfish-medusae • Hydrozoans-may have both forms

6. Cnidarian diversity • Fig. 30.4

7. Cnidarians cont’d • Hydra • Representative organism (Class Hydrozoa) • Freshwater, attaches to rocks, leaf litter • Small tubular polyp, sac-like body plan with a single opening • Outer tissue layer – epidermis from ectoderm • Inner layer – gastrodermis from endoderm • Longitudinal and circular muscle fibers present • Diffuse nerve net between layers

8. Cnidarians cont’d • Digestion begins in gastrovascular cavity, completed in cells • Can reproduce sexually and asexually (budding) • Sexual reproduction- hydra develops an ovary or testis in body wall-produces gametes

9. Anatomy of Hydra • Fig. 30.5

10. Invertebrates: Phylum Platyhelminthes • Flatworms • Bilateral symmetry, three germ layers, acoelomate • Mesoderm gives greater complexity • Muscles, excretory, reproductive, and digestive systems in some • Respiration by diffusion and circulation

11. Platyhelminthes cont’d • Class Turbellaria - Planarians • Free-living flatworms • freshwater, feed on small living and dead organisms • Ladder-like nervous system • Ganglia and eyespots anterior • Auricles – chemosensitivereceptores • Digestion: • Feed through muscular pharynx • Specialized cells for excretion: flame cells

12. Platyhelminthes cont’d • Class Turbellaria - Planarians cont’d • 3 muscle layers- circular, longitudinal, and diagonal • Allows for more complex movements • Cephalization • Organized to have an anterior end and a posterior end • Hermaphroditic

13. Planarian • Fig. 30.6

14. Parasitic Platyhelminthes • Class Cestoda (Tapeworms) • Internal parasites as adults • Body Structure • Tegument: tough outer covering • protect from host’s enzymes • Scolex - head • Barbs/hooks for attachment • Proglottids: segments • Each contains organs of both sexes • Lack a digestive system- why?

15. Parasitic Platyhelminthescont’d • Class Cestoda (Tapeworms) (cont’d) • Reproduction • Fertilization is internal • proglottids filled with fertilized eggs are called gravid • Gravid proglottids drop off and pass out in feces • Ingested by intermediate host • larvae become encysted • Intermediate host is then eaten by definitive host • Larvae mature to adults • Representative Organism: Taneasolium • Pork tapeworm

16. Life cycle of a tapeworm, Taenia • Fig. 30.7

17. Parasitic Platyhelminthescont’d • Class Trematoda - Flukes • Endoparasites of many species • Body Structure • Tegument • Oral sucker and posterior sucker • Digestion • Well-developed digestive canal

18. Parasitic Platyhelminthescont’d • Class Trematoda - Flukes cont’d • Muscles and excretory system much like free-living flatworms • Poorly developed sense organs- why might that be? • Reproduction • Hermaphroditic • Complex life cycle involving two intermediate hosts

19. Parasitic Platyhelminthescont’d • Class Trematoda - Flukes cont’d • Representative Organism: Clonorchis sinensis • Liver Fluke • Transmission • Snails ingest eggs • Develop in to larvae, which leave the snail and burrow into muscles of a fish • Humans ingest fish • Larvae moves into bile ducts where adults develop • Eggs pass out of human in feces, cycle continues

20. Invertebrates: Phylum Nematoda • Roundworms • First appearance of • Tube-within-a-tube body plan • 2 openings, mouth and anus • Body Cavity • Pseudocoelomates • Pseudocoel -filled with fluid, acts as hydrostatic skeleton • Many species; some are free-living in soil and water, others are parasitic

21. Coelom structure and function • Fig. 30.8

22. Parasitic Nematodes • Ascaris • Move with whip-like motion • Intestinal parasites in many animal species • Females are much longer than males and highly prolific • Eggs enter host in uncooked vegetables, soil, or feces • Larvae burrow out of intestine and migrate to heart and lungs • Larvae are coughed up and swallowed • Mature to adults in intestines • Estimated to infect 25% of world population

23. Roundworm anatomy • Fig. 30.9

24. Parasitic Nematodes cont’d • Trichinella spiralis • the trichina worm • Causes trichinosis • Humans contract the worm by eating undercooked pork • Larvae migrate out of intestines and form painful cysts in the muscles

25. Parasitic Nematodes cont’d • Wuchereria bancrofti • filarial worm that causes elephantiasis • Migrates into lymphatic vessels and prevents lymph drainage • Edema occurs

26. Parasitic Nematodes cont’d • Pinworms and hookworms • Roundworm parasites which cause problems in children • Much more common in U.S. • Pinworms are primarily an annoyance • Hookworms cause skin irritations and in some cases debilitating disease